diff --git a/modules/user/user.admin.inc b/modules/user/user.admin.inc
index afaddeb..53ade47 100644
--- a/modules/user/user.admin.inc
+++ b/modules/user/user.admin.inc
@@ -712,7 +712,12 @@ function user_admin_permissions($form, $form_state, $rid = NULL) {
 
   // Have to build checkboxes here after checkbox arrays are built
   foreach ($role_names as $rid => $name) {
-    $form['checkboxes'][$rid] = array('#type' => 'checkboxes', '#options' => $options, '#default_value' => isset($status[$rid]) ? $status[$rid] : array());
+    $form['checkboxes'][$rid] = array(
+      '#type' => 'checkboxes',
+      '#options' => $options,
+      '#default_value' => isset($status[$rid]) ? $status[$rid] : array(),
+      '#attributes' => array('class' => array('rid-' . $rid)),
+    );
     $form['role_names'][$rid] = array('#markup' => check_plain($name), '#tree' => TRUE);
   }
 
diff --git a/modules/user/user.permissions.js b/modules/user/user.permissions.js
index 4ef576c..988820e 100644
--- a/modules/user/user.permissions.js
+++ b/modules/user/user.permissions.js
@@ -5,34 +5,64 @@
  */
 Drupal.behaviors.permissions = {
   attach: function (context) {
-    $('table#permissions:not(.permissions-processed)').each(function () {
+    var self = this;
+    $('table#permissions').once('permissions', function () {
+      // On a site with many roles and permissions, this behavior initially has
+      // to perform thousands of DOM manipulations to inject checkboxes and hide
+      // them. By detaching the table from the DOM, all operations can be
+      // performed without triggering internal layout and re-rendering processes
+      // in the browser.
+      var $table = $(this);
+      if ($table.prev().length) {
+        var $ancestor = $table.prev(), method = 'after';
+      }
+      else {
+        var $ancestor = $table.parent(), method = 'append';
+      }
+      $table.detach();
+
       // Create dummy checkboxes. We use dummy checkboxes instead of reusing
       // the existing checkboxes here because new checkboxes don't alter the
       // submitted form. If we'd automatically check existing checkboxes, the
       // permission table would be polluted with redundant entries. This
       // is deliberate, but desirable when we automatically check them.
-      $(':checkbox', this).not('[name^="2["]').not('[name^="1["]').each(function () {
-        $(this).addClass('real-checkbox');
-        $('<input type="checkbox" class="dummy-checkbox" disabled="disabled" checked="checked" />')
-          .attr('title', Drupal.t("This permission is inherited from the authenticated user role."))
-          .insertAfter(this)
-          .hide();
-      });
+      var $dummy = $('<input type="checkbox" class="dummy-checkbox" disabled="disabled" checked="checked" />')
+        .attr('title', Drupal.t("This permission is inherited from the authenticated user role."))
+        .hide();
 
-      // Helper function toggles all dummy checkboxes based on the checkboxes'
-      // state. If the "authenticated user" checkbox is checked, the checked
-      // and disabled checkboxes are shown, the real checkboxes otherwise.
-      var toggle = function () {
-        $(this).closest('tr')
-          .find('.real-checkbox')[this.checked ? 'hide' : 'show']().end()
-          .find('.dummy-checkbox')[this.checked ? 'show' : 'hide']();
-      };
+      $('input[type=checkbox]', this).not('.rid-2, .rid-1').addClass('real-checkbox').each(function () {
+        $dummy.clone().insertAfter(this);
+      });
 
       // Initialize the authenticated user checkbox.
-      $(':checkbox[name^="2["]', this)
-        .click(toggle)
-        .each(function () { toggle.call(this); });
-    }).addClass('permissions-processed');
+      $('input[type=checkbox].rid-2', this)
+        .bind('click.permissions', self.toggle)
+        // .triggerHandler() cannot be used here, as it only affects the first
+        // element.
+        .each(self.toggle);
+
+      // Re-insert the table into the DOM.
+      $ancestor[method]($table);
+    });
+  },
+
+  /**
+   * Toggles all dummy checkboxes based on the checkboxes' state.
+   *
+   * If the "authenticated user" checkbox is checked, the checked and disabled
+   * checkboxes are shown, the real checkboxes otherwise.
+   */
+  toggle: function () {
+    var authCheckbox = this, $row = $(this).closest('tr');
+    // jQuery performs too many layout calculations for .hide() and .show(),
+    // leading to a major page rendering lag on sites with many roles and
+    // permissions. Therefore, we toggle visibility directly.
+    $row.find('.real-checkbox').each(function () {
+      this.style.display = (authCheckbox.checked ? 'none' : '');
+    });
+    $row.find('.dummy-checkbox').each(function () {
+      this.style.display = (authCheckbox.checked ? '' : 'none');
+    });
   }
 };